Safety switch



Nov. 3, 1959 H. GARBERs 2,911,503

SAFETY SWITCH Filed Nov. 21, 195e vwxmmm HELMUT GARBERS if /awm f /o-uAffameys United States Patent O SAFETY SWITCH Helmut Garbers,Neumunster, Germany, assignor to Licentia Patent-Verwaltungs-G.m.b.H.,Hamburg, Germany Application November 21, 1956, Serial No. 623,585

Claims priority, application Germany November 21, 1955 5 Claims. (Cl.200122) This invention relates to automatic safety switches. More inparticular this invention relates to automatic safety switches with heatactuated contacts consisting of bi-metal strips or other devicesresponding to a heat actuation by a snap switching action.

It is known in the art to control electrical appliances and prevent themfrom being destroyed by overloading. To achieve this purpose apparatushave been devised consisting mainly of a control member and a switchingmember. Both members are provided with contacts. An overloading of theparticular electrical appliance results in an actuation of the controlmember and this actuation is transmitted to the switch member by meansof the contacts whereby the switch member is caused to switch oi theelectrical appliance.

In most of these devices the switch means do not reassume their initialposition so as to close the circuit and restart the operation of theelectrical appliance after the condition causing the interruption of theswitch has subsided. Rather, after the temporary overloading conditionhas actuated the control member in the known switch means and the memberhas once brought the switch means into the switch-oli position, thisposition is retained even after the heat-actuated member has cooleddown.

It is true that, in many instances, it is undesirable to provide for anautomatic reclosing of the circuit because the switching in of theappliance is to be supervised and effected by a supervising person.

For these reasons the afore mentioned safety switch devices known in theart have been provided with an independently operable switch meansconsisting of a push button or a key by means of which the snap memberof the switch can be readjusted to its initial position thus closing thecircuit at will. These known safety devices suer from the considerabledisadvantage that the snap device can be readjusted to close the circuiteven though the initial actuating cause, i.e. the overload condition ofthe electrical appliance and the resulting production of heattransmitted to the control member has not yet subsided. As a result, theprotection of the electrical appliance offered by the automaticoperation of the control member and the snap switching member can bein-terfered with by the supervising person through the independentlyoperatable push button or key device. As a result, the electricalappliance can be destroyed by holding the circuit closed contrary to thetendency of the control member, for example a bi-metal strip, to effectthe switch-off through the snap switch.

It is an object of the present invention to provide for an improvedsafety switch.

It is a further object of the present invention to provide for animproved safety switch wherein the automatic switching olf operationcannot be interfered with against the tendency of the control member toswitch olf the appliance protected by the switch.

These objects are achieved and the problem for which the devices knownin the art are unsatisfactory, is solved by the following .device of thepresent invention. The

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push button or key means is provided with an energystoring memberadapted toV store up a determined amount of energy produced by pressingthe key or the button. This pent-up energy is sufficient to produce aforce,

whereby the position of the snap switching means canV be changed if onlythe inertia of the latter has to be overcome. It is not suicient,however, to change the position of the 4latter whenever it is supportedin its interrupted position by an additional force imparted to it by theheat actuated control member. As a consequence, it is possible to resetthe snap switch to its initial position by pressing the key if thecircuit is not overloaded, and hence there is no thermal energyproduced; but it is not possible to reset the switch, whenever theinertia of the switch is supported by the force of the heat-actuatedcontrol member.

The invention will be more fully comprchended by the following detaileddescription taken in conjunction with the accompanying drawings wherein,

Figure l is a sectional elevational view of the apparatus of theinvention showing the first end position of the switch, control and keydevices.

Figure 2 is a sectional elevational view of the appalratus of theinvention showing the second end position of the switch, control and keydevices. v

. Within the casing consisting of an upper part 11 and a lower part 12there is arranged a snap lever 1, 2, 3 provided with a contact 33 andconstituting the switch device. Also Within the casing and in paralleldirection below the snap lever there is arranged a bi-metal strip 4having a contact 34 directly opposed to the contact 33 of the snap lever1, 2, 3 constituting the control device.

The casing has openings 13 admitting air and thus allowing warm air toreach the bi-metal strip 4.

The snap switching device comprises a lever 1 being supported at one endin the recess 10 of a screw 9. The other end of the lever 1 isdisplaceably positioned in a cap 2. A second cap 3 is supported in therecess 15 of a support member 14 with its end 3a opposite to the endfacing the rst cap. Between cap 2 and cap 3 there is arranged apressurerspring 32. The two end positions of the snap switching deviceare shown in Figure 1 and Figure 2, respectively.

In the upper part 11 of the casing there is mounted a cylinder shapedhull 36. This hull may form an integral part of the upper part of thecasing 11. The hull is provided with a threading 20 engaged by two screwnuts 18 and 19 by means of which the entire device can be clamped to awall 35. A cylindrical body 7 is slidably positioned within thecylindrical hull 36. A piston 17 mounted on bolt 5 is positioned withinthe cylinder 7. A spring 8 is arranged between the surface of the pistonand the cover plate 21 screwed to the upper end of the cylindrical body.The bolt 5 leads into the interior of casing 12 and is provided with arst annular flange 6 and a second or head flange 16 serving as a pestleand cooperating with the bi-metal strip 4.

The bolt 5 is led through a corresponding hole in the snap lever 1 whichlever is joined to the circuit by means of a ilexible conductor 27connected with the current junction 24. The bi-metal strip 4 is fastenedto the lower part of the casing 12 by screw 28. Additional junctions 25and 26 are connected with the heater windings 29 and 30 coiled aroundthe bi-metal strip 4 and also lead to the outside of the casing wherethey constitute the connections for the supply line 40. The recessbearing 10 can be adjusted by turning the screw 9 in order to adjust theinitial position of the snap switching means 1, 2, 3. By turning thescrew 9 to withdraw the same outwardly from the casing the initialposition of the lever` 1 and thereby the entire lever switching device1, 2, 3

is raised, and thereby a greater amount of heat and a greater bending ofthe .bi-metal strip corresponding to a higher temperature will stillretain the contact 34 in contacting position withcontact 33. By turningthe screw 9 it is thus possible to regulate the contact means 1, 2, 3 soas to correspond to a predetermined value. The adjustment of the screwas well as its insertion into the casing is performed through theopening 23 which can be covered by a plate 2,2 after the screw has beeninserted or its adjustment has been completed.

The Various junctions 24, 25, 26 serve the function of obtaining avarying heating of the bi-metal strip, according to whether anelectrical appliance must be controlled at the switch-in moment orduring its operation. For this purpose only the Winding 29 or both thewinding 29 and the winding 3), or only the winding 3) can be connectedto the circuit. The end of the entire winding is connected with thebi-metal strip at 31. rThe connection 31 can be obtained by spotWelding. The entire circuit comprises the windings or at least one ofthe windings, 29 and 30, the bi-metal strip 4, the contacts 34 and 33,the contact lever 1, the exible connection 27 and the line 24.

The operation Whenever an excessively elevated electric current resultsin a heating of the bi-metal strip 4 causing the same to bend, therebybringing the contact means 1, 2, 3 into the position shown in Figure 2,the contacts 33 and 34 are being separated. At the same time the bolt 5is moved in upward direction and consequently the key means described indetail further above with its cover 21 protrudes from the hull 36. Assoon as the bi-metal strip 4 has cooled down and reassumes its initialposition shown in Figure 1 of the drawings the contact lever 1, Z, 3remains in the position shown in Figure 2. It can be reset to theposition of Figure 1 by pressing the key 21 into the cylindrical shapedbody 7. If this is done, the flange 6 of the bolt 5 takes along thecontact lever 1 and results in a snap switching action of the same.

As long as the bi-metal strip 4 is continued to be heated the bent upposition of the strip will be maintained. Since the force exerted by theheated strip upon the top part 16 of the bolt 5 is greater than theforce produced by the spring 8 and imparted to the piston 17 on theother end of bolt 5, the pressing down of the key does not alter theposition of bolt 5 but only results in energizing the spring 8 bypressing the same against the piston 17 of bolt 5. As a consequence thebi-metal strip remains in its bent up position as shown in Figure 2 anda snap switching action of the lever 1, 2, 3 is prevented. For thesereasons a pressing of the key does not result 1n a switching of thelever and a closing of the circuit which has been interrupted by theheat actuation 0f the bi-metal strip 4, as long as this actuation of thebi-metal strip by the excessive heat prevails. It is, therefore,impossible for an operating person, to interfere by means of the keydevice, with the automatic interruption of the circuit caused by anoverloading of the circuit and the electrical appliance, and any damageto the electrical appllance by interfering with the automatic controloperation is avoided.

The invention can be applied particularly to electrical householdappliances but it is not confined to an application thereto. It can beused in all electrical devices and appliances where the bi-metal stripis excited only by heat entering from the outside without special heatwindings. By applying the present invention, for example, to the motorof an overloaded household appliance, it will become impossible to forcethe appliance into a continued operation and thereby damage the same.

It will be understood that this invention is susceptible to modificationin order to adapt it to different usages and conditions, and,accordingly; it is desired to compre- 4 hend such modifications withinthis invention as may fall within the scope of the appended claims.

What I claim is:

1. A safety switch for closing and breaking contact in an electriccurrent circuit, comprising in combination, a switch member, anautomatic control member which is deformable automatically in responseto a predetermined heat stimulus and, when deformed thereby, actuatingsaid switch member to interrupt said circuit, and

key means operable at will independently of `said stimulus d andcomprising a reset member comprising a push button which is movable toand fro in the direction of the deflection of said switch member andoperatively associated with bothk said switch member and said controlmember in such a manner Ythat when said push button is moved in onedirection it engages only said control member and that when said pushbutton is moved in the opposite direction it engages both said switchmember and said control member, said push button being adapted toactuate said switch member to switch back to circuit-closing position,upon operation of said key means, only while said control member is notdeformed.

2. A safety switch for closing and breaking contact in an electriccurrent circuit, comprising in combination, a switch member, anautomatic control member which is deformable automatically in responseto a predetermined heat stimulus and, when deformed thereby, actuatingsaid switch member to interrupt said circuit, and key means operable atwill independently of said stimulus and comprising a push button resetmember engaging said control member at all times and being adapted tocause said switch member to switch back to circuit-closing position,upon operation of said key means, only while said control member is notdeformed, means for storing energy connected to said key means, saidenergy storing means being capable of absorbing a predetermined amountof energy produced by operating the key, which absorbed amount isequivalent to the inertia of said switch member taken alone and inferiorto the sum of said inertia andthe energy produced by said control memberwhen being deformed and acting upon said push button reset member inresponse to a stimulus.

3. A safety switch for closing and breaking Contact in an electriccurrent circuit, comprising in combination, a switch member, anautomatic control member which is deformable automatically in responseto a predetermined heat stimulus and, when deformed thereby, actuatingsaid switch member to interrupt said circuit, and key means operable atwill independently of said stimulus and comprising a reset memberengaging said control member at all times, said reset member comprisinga bolt, an annular flange, and a head flange, said annular liange beingmounted substantially at the middle portion of said bolt, said headflange forming the head end of said bolt, said bolt cooperating withsaid switch member through said annular flange and cooperating with saidcontrol member through said head flange, means for storing energyconnected to said key means, said energy storing means being capable ofabsorbing a predetermined amount of energy produced by operating thekey, which absorbed amount is equivalent to the inertia of said switchmember taken alone and inferior to the sum of said inertia and theenergy produced by said control member when being deformed and actingupon said reset member in response to a stimulus, said key means therebybeing adapted to cause said switch member to switch back tocircuit-closing position, upon operation of said key means, only whilesaid control member is not deformed.

4. A safety switch for closing and breaking contact in an electriccurrent circuit, comprising in combination, a

switch member, an automatic control member which is deformableautomatically in response to a predetermined said switch member throughsaid annular flange and cooperating with said control member throughsaid vhead flange, said key means being adapted to cause said `switchmember to switch back to circuit-closing position, upon operation ofsaid key means, only while said control member is not deformed. Y l

5. A safety switch as described in claim 1, wherein said switch meanscomprise a switch lever, a rst cap, a'spring and a second cap, said rstcap being Vhingedly mounted to said switch lever, said second capconnected to said iirst cap and said spring being interposed betweensaid rst and said second cap, an end bar, lsaid end bar having arecessed upper portion, the tip of said second cap v being supportedwithin said recess, an adjusting screw, said screw having a recessedlower portion, the other end of said lever being positioned in saidrecess of said screw, and being lowered or raised by turning saidadjusting screw in one direction or the other, respectively.

References Cited in the file of this patent UNITED STATES PATENTS1,315,466 kCavanagh `Sept. 9, 1919I 1,743,073 Simmons Jan.r 7, 19301,859,985 Riedel May 24, 1932 1,952,129 Hardman Mar. 27,` 1934 2,210,084Kuhn et al. Aug. 6, 1940 2,262,205 Schachtner Nov. 11, 1941 2,318,076Johns May 4, 1943 2,446,307 Shaw Aug. 3, 1948 2,515,528 Rothwell July18, 1950 2,521,277 Aubert Sept. 5, 1950

